Brains are the atheist equivalent of souls. This particular brain is only fetus-brain sized so it doesn’t trigger any worries of morality in me to create it and terminate it in a lab experiment, but we should be wary of doing this sort of thing on a larger brain that starts to approach born-baby-sized brains. If they got this far it’s not much of a stretch to contemplate that the ability to grow a full size human brain in the lab may appear down the road in the future.

If you start from the materialist viewpoint that there is no such thing as a soul then the physical brain is all that’s left as the be-all, end-all of what it is to be a human with full human rights. If the experiment could be taken further to make a full sized, fully developed human brain, we’d have no choice but to insist that brain gets to have the same protections and rights as a born baby.

And that would severely curtail what sort of experimental usefulness the brain would have. You shouldn’t be allowed to just do whatever to like to the brain to see what would happen.